1. Field of the Invention
The present invention is directed to a method of channel allocation for a communication connection to a radio interface in a mobile communication system with spatial subscriber separation, wherein K.sub.ges existing communication connections are already handled via the radio interface.
2. Description of the Prior Art
Channel allocation methods for mobile communication systems with spatial subscriber separation are known from M. Tangemann, "Near-Far effects in adaptive SDMA systems", 6th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC 95), 1995, Toronto, Canada, pp. 1293-1297. A plurality of communication connections can be handled in a common channel in such SDMA (space division multiple access) systems, wherein the channel is described by a frequency band and, potentially, a time slot in SDMA/TDMA (time division multiple access) systems. To that end, adaptive antennas are utilized at the transmission side; for example, in base stations of mobile radiotelephone networks. As a result of these adaptive antennas, a plurality of emission lobes matched by beam shaping to the respective position of the receiving radio station (for example, mobile stations of mobile radiotelephone networks), can be formed. The spatial resolution that is used for the separation of subscriber signals occurs on the basis of these mutually independent emission lobes.
The transmission path from a base station to a mobile station is referred to as "downlink", whereas the transmission path from a mobile station to a base station is referred to as "uplink." The spatial subscriber separation by beam shaping is typically utilized in the downlink. A spatial subscriber separation yields a gain in capacity in mobile communication systems since a greater plurality of communication connections, given an unaltered bandwidth required, can be handled in addition to other subscriber separation methods TDMA, FDMA or CDMA.
The problem of selecting a suitable channel for an added communication connection due to a call setup or a handover from a neighboring cell arises in mobile communication systems with SDMA subscriber separation. It is known from M. Tangemann, "Near-Far effects in adaptive SDMA systems", 61th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC 95), 1995, Toronto, Canada, p. 1294, to guarantee a predetermined signal/noise ratio wherein a common channel is allocated to spatially widely separated mobile stations of a transmission power group. When, however, the direction estimate for the positions of the mobile stations that precedes the channel allocation is imprecise, this channel allocation leads to a disadvantageous sensitivity of the spatial subscriber separation. The signal/noise ratios actually achieved fluctuate greatly.
Further allocation methods, wherein a separability test and a calculation of weighting matrices for existing communication connections are implemented, are known from F. Farsakh, J. A. Nossek, "A real time downlink channel allocation scheme for an SDMA mobile radio system", PIMRC'96, Taipeh, Taiwan, 1996. A channel-related consideration of transmission characteristics is thereby not implemented such that the characteristics defined in common for all channels do not form a stable basis for an allocation strategy. The entire beam shaping algorithm is to be respectively applied anew for calculating the weighting matrices. This leads to a considerable calculation-oriented outlay.